The invention relates to a method for the process management of a mold-filling process of an injection molding machine.
Approaches are known from the prior art for compensating individual process fluctuations, which have a negative influence on the mold-filling process of an injection molding machine and are caused by interfering influences.
A method for quantifying process fluctuations in an injection process of an injection molding machine is known from EP 2 583 811 A1. This method uses reference curves of characteristic variables along a path or a multiplicity of positions (x), which covers an injector of an injection molding machine during an injection process. The characteristic variables can be pressure values, e.g. an injection pressure, a melt pressure, an internal mold pressure or an internal mold temperature. At least one of the characteristic variables is measured for a multiplicity of positions of the injector during an injection process, so that a measurement function results. Furthermore, the method disclosed in this published document uses at least one mathematical transformation, by means of which the measurement function created in the measurement is mapped onto the reference function of the characteristic variable in the best possible manner. To this end, the method uses a freely selectable transformation parameter, which is determined in such a manner that an image function resulting from the measurement function matches the reference function in the best possible manner with respect to a predetermined error measure. A process fluctuation is assigned to the transformation parameter. The process fluctuation is qualified with reference to the reference function under the use of at least one transformation parameter. Fluctuations of the shot volume and fluctuations of the pressure requirement for filling a cavity are specified inter alia as possible process fluctuations.
It is known from DE 35 24 310 C1, for the regulated operation of plastic injection molding machines, to call upon the injection operation for managing the injection molding process. The aim is to move a movement of the screw, for example a first screw A and a second screw B with different screw characteristics, in a regulated manner for a constantly equal injection duration. A final value for the screw path and the holding pressure profile are stored and called upon for an adjustment factor. Process management via the injection operation has the disadvantage however that it is strongly characterized by irregularities in the start-up phase of the injection process and cannot compensate an uneven closing behavior of a non-return valve.
A method is known from DE 10 2007 061 775 A1, in which the temporal course of the mold internal pressure is measured during the holding-pressure phase of an injection-molding process. At least one non-time-dependent characteristic variable is determined from this temporal curve of the mold internal pressure, for which this or each characteristic variable is compared with a stored characteristic-variable set-point value and for which, on the basis of the comparison result, an adjusted holding pressure value for a subsequent injection-molding process is automatically determined. In this method, learning is therefore carried out in a preceding injection-molding process for a subsequent injection-molding process, wherein a correction of a changing characteristic-variable value takes place in the context of a holding-pressure adjustment.
From DE 10 2005 032 367 A1, an approach is followed such that the time, which the melt requires during the injection process up to a sensor in the cavity, is monitored and the viscosity of the melt is adjusted in the event of changes or differences in this time which are deemed to be too large. To adjust the viscosity, it is suggested to change the temperature of the melt. This method makes use of the discovery that the flow rate of the melt can be changed by a change in the viscosity of the melt.
Approaches of this type from the published documents mentioned for compensating interfering influences often relate to a reference curve of one or a plurality of process variables. This disadvantageously has the consequence that it is necessary to permanently make an adjustment with respect to a reference. This often entails further manual corrections if the production conditions, e.g. the environmental conditions or the material qualities of the plastic to be processed, change beyond a certain extent. In addition, at least certain of the approaches mentioned appear complicated and cost intensive with regards to their technical feasibility.